Isobel Campbell: Lone star

Isobel Campbell certainly knows how to make an entrance. It's midday and she's dressed to kill as she walks into Glasgow's Centre for Contemporary Arts in a scoop-necked grey dress that displays a bounteous decolletage, accessorised by shiny red patent-leather stilettos with matching red belt and woollen wrap. A smear of misapplied mascara at the corner of one eye enhances the not unpleasing impression of slightly soiled sophistication.

It's just the contradiction that informed Campbell's work as the creator (and curator) of one of the year's most arresting records, the Mercury Music Prize-shortlisted Ballad Of The Broken Seas. A collection of dark duets with Mark Lanegan that conjures the ghosts of Lee Hazelwood and Nancy Sinatra, it contrasted her whispery angelic voice and dark lyrics against the world-weary rasp of the former Screaming Trees and Queens Of The Stone Age singer.

Previously best known for embellishing twee indie collective Belle & Sebastian with shimmering cello and featherlight vocals, Campbell - who wrote and produced Ballad Of The Broken Seas - seemed finally to have found her true voice.

It's taken her the best part of her 30 years to find it. There was little suggestion in B&S (as she refers to them) that she would ever move into the spotlight. Three subsequent "solo" albums, two of them under the pseudonym of The Gentle Waves, reinforced the idea that she would remain content to paddle in the shallow waters of fey indie-folk.

Now comes Milkwhite Sheets, a collection of acoustic folk songs, both traditional and original. Musically, it has little in common with the spectral blues-rock of Ballad... but listen closely and these "psychedelic lullabies" reveal a quietly subversive underbelly. Perhaps it was always there. "They used to call me the dark heart of Belle and Sebastian," says the singer with a girlish giggle.

Campbell, who turns out to be bubbly, garrulous and prone to fits of self-mocking laughter, makes no pretence to having grown up listening to traditional music around the hearth of a Scottish home. "No. I grew up with Fleetwood Mac and Van Morrison. Then I discovered The Beatles when I was 14, then The Kinks, and that was it."

The new album, she says, is "kinda like a hobby album" that she began while waiting for Lanegan to record his vocals for Ballad... - a process conducted by post in the manner of Elton John and Bernie Taupin. "I'd write and record the songs with my vocals and then send them off to him by Fed-Ex and wait for him to send them back with his parts," she says. "Which was usually a matter of weeks."

For inspiration, she immersed herself in Harry Smith's seminal Anthology of American Folk Music, but was never going to turn into a fully fledged finger-in-the-ear folkie. "There's so much folk music I can't listen to - the stuff that's more Arran sweaters and drinking ale than anything else," she laughs. "It's the heart and soul of folk music I love - natural earthy songs that belong to the people. Folk music's like punk, the first rebel music."

Despite her ethereal voice and mellifluous music, Campbell claims she has always been drawn to the wild side; as was finally demonstrated with Ballad. This had already been noted by Lanegan who, when recently asked what drew him to collaborate with Campbell, identified the darkness in her songs. "The music I love has always had to have an edge," she agrees. "If something's slick and bland, I'm not interested." As if to prove the point, she pushes away her bowl of soup, complaining that it's too bland - "like baby food".

She remains disappointed that, despite the success of their album, which has sold around 100,000 copies worldwide - easily the best of her career - she has never yet performed live with Lanegan. She has played around 50 dates in Europe and America based around that album, but has used as a stand-in Eugene Kelly, a fellow Glaswegian and former member of Kurt Cobain's favourite band, The Vaselines. It's a tall order to ask Kelly to replicate the drug-addled, whisky-soaked, nicotine-stained growl of Lanegan but he has been taking extraordinary steps to achieve a reasonable facsimile. "Eugene gets in character in the dressing room," she reports. "He comes over all funny, almost like the Incredible Hulk but not really... The incredible bulk, maybe." Once again she bursts out laughing.

This month Campbell attended the Mercury Music Prize ceremony but says awards shows are not really her thing, and anyway she spent most of the night being interviewed upstairs while her record company enjoyed the show. Her trophy, she adds, is still in an unpacked suitcase. It was not the first time she had been nominated for an award. In 1999 Belle & Sebastian achieved some sort of notoriety at the Brit Awards by snatching the Best Newcomers gong from under the noses of the nation's favourite pop act, Steps. But Campbell wasn't there. "The tickets were too expensive - about £500 - and I was still at Uni," she recalls. "Richard our drummer and Mick the trumpet player trotted off to London for it and came back with all these great stories. They said that as soon as they went on the red carpet all the photographers stopped flashing. And when they got up to collect the award everyone was like: 'Who are they?' I think Richard said in his speech: 'I'm Belle and he's Sebastian'."

That B&S should triumph in an internet vote ought not to have been entirely surprising in view of their strong student fan base. But the outraged pop pundits at The Sun were having none of it, mostly on the grounds that none of their readers had even heard of Belle & Sebastian. The result, therefore, must have been a fix. "I didn't even vote for myself - I didn't have e-mail," protests Campbell, who still doesn't have a mobile phone. The Sun decided to right the wrong by running its own readers' poll in which - surprise surprise! - Steps came out on top, though B&S still came in at a respectable third place.

Still, the Brit Award did boost Belle & Sebastian's career, though Campbell accepts that they failed to capitalise on their 15 minutes of nationwide fame. "I think that if we'd toured at that point we would have cleaned up," she says. "But Chris and I were at Uni. Most people in our position would have gone: 'Fuck that, we're going on tour', but we were like: 'Oh, we've got to get our degrees'."

After finishing her music degree at Strathclyde University, Campbell eventually quit the band in 2002; not an easy decision after six and a half years' service.

"It was difficult. There were quite a lot of us and we were like a family. I just wanted to be the master of my own destiny. I could have taken the easy option: could have stayed, could have put my feet up, drunk myself into a stupor and not had to worry about paying my rent. But it wasn't enough for me. I like to flit about between projects."

She's certainly done plenty of that. Before her departure she had recorded two melancholic folk-pop albums, Green Fields Of Foreverland and Swansong For You, under the pseudonym of The Gentle Waves. They were followed in 2003 by the critically acclaimed Amorino, the first album to be released under her own name. There was a considerable gap before the release of Ballad which, she concedes, is closest to her true self.

She has recently been collaborating with another gravel-voiced maverick, Howe Gelb, on what may yet become a sequel to the Lanegan album. She is excited about a forthcoming trip to his home in Arizona and has performed with Gelb and his band Giant Sand. Typically, she is undecided about what to do next. "Half of me wants to do that and half of me wants to make a modern-day Rumours," she laughs. "Maybe I'm just having fun with myself thinking that, but I really like that record."

As for her personal future, she tempers her hopes with a natural pessimism. "Good things, hopefully," she says uncertainly. "But I'm a glass half-empty person. I cannae help it, that's my Scottishness coming out. But when I move to California that might all change." She is not, of course, moving to California at all, but dreams of a change. "I love my home but I'd like to move. I need to be more engaged in where I'm living."

Just a few days ago, when she returned to Glasgow, she went out for dinner with her mother, who took her to the supermarket on the way home, so she could stock up her house with supplies.

"She was making fun of me 'cos I was banging on about cleaning products. She said: 'I don't think you're going to make another record, you're going to have a cleaning company.' But I'm not actually much good at mopping floors. I talk about cleaning all the time but I hardly ever do it because I really like listening to music while I clean. I did my classic the other day: I started, I hovered, and started listening to Closing Time [by Tom Waits] again and the song "Martha" always gets me. Then I think the phone rang and I got distracted."

She has few other interests outside music, she says, but feels content at the age of 30. "I'm not exactly where I'd like to be - I need a new manager - but I'm definitely in the right ball park. I feel a burning passion for what I do. Maybe I'll give it up and have babies at some point, but at the moment I'm really driven to do it. Right now my albums are my children and they're quite unruly and difficult. We'll see." She looks up with those limpid eyes shining. "I really want to make great records."

'Milkwhite Sheets' (V2) is released on 23 October